Electromagnetic indicator



May 11, 1965 Filed Nov. 8, 1960 R. F. CASEY ELECTROMAGNETIC INDICATOR 2 Sheets-Sheet l FIG.

lNVENTfiR. ROBERT F. CASEY BY 11 JAM/Am ATTORNEYS May 11, 1965 R. F. CASEY 3,183,503

ELECTROMAGNETIC INDICATOR Filed Nov. 8, 1960 2 Sheets-Sheet 2 INVEN TOR. ROBERT F. CASEY W, MW

ATTORNEYS United States Patent l 3,183,503 ELEQTROMAGNETIC INDICATOR Robert F. Casey, East Acton, Mass assiguor to Arthur D. Little Inc., Cambridge, Mass, a corporation of Massachusetts Filed Nov. 8, 1960, Ser. No. 67,956 2 Claims. (Cl. 340-378) The present invention relates generally to data display systems and specifically to compact electromagnetic data indicators which selectively position preselected characters or indicia in response to external electrical excitations.

The present invention is an improvement on electromagnetic indicators of the type disclosed and claimed in US. Patent No. 2,943,313 and my copending application, Serial No. 1,320, for Electromagnetic Indicator.

Electromagnetic indicators of the type to which the present invention pertains comprise an electromagnetic structure which is selectively enregizable to produce any one of a pluarlity of discrete electromagnetic field orientations, and a magnetic element whose motion and position is governed by the selected field orientation. Carried. by or otherwise coupled to this magnetic element is a character-bearing member having appropriate numbers, letters, or other symbols. Generally, this type of indicator is associated with a viewing window for visual observation of the chosen character. When the electromagnetic structure is energized to produce a predetermined electromagnetic field orientation, the magnetic element will rotate so as to align itself with the magnetic field vector and the character member will rotate with the magnetic elenmt so as to position the desired character at the viewing window. Generally, two closely adjacent, magnetically determined stable positions are available for the magnetic element and the character bearing member for each character to be displayed, one stable position being determined by the electromagnetic structure when electrical excitation is applied thereto and the other being determined by an independent static magnetizable member which coacts with the magnetic element associated with the character-bearing member in the absence of electrical excitation. As will be more apparent hereafter, only the first position is necessary for the present invention.

In practice, it has been determined that when the rotor magnet rotates to a new position determined by the particular electromagnetic field orientation which is established, the magnet tends to overrun the position established by the electromagnetic structure. Consequently, it must reverse its course and swing back toward the desired equilibrium position. However, the magnetic element will tend to override the equilibrium position on its reverse swing. In fact, it will oscillate for a short period of time relative to the desired equilibrium position before it comes to rest. The interval of oscillation (commonly called hunting time) is dependent upon the magnitude of the overrun on the initial swing of the magnetic element toward the equilibrium position. The greater the overrun, the greater the number of oscillations and the longer the hunting time. Although these electromag;

netic indicators are fast-acting devices, their tendency to hunt has limited their use in certain high-requirement situations.

Accordingly, the object of the present invention is to provide means in an electromagnetic indicator of the type referred to which functions to reduce the tendency of the magnetic device to oscillate about its equilibrium position, whereby the magnetic device and the associated character member will rapidly assume the desired equilibrium position. The means for reducing the tendency of the magnetic element to hunt a specific equilibrium position takes 3,183,503 Patented May 11, 1965 the form of a clamping device which rotates with the magnetic element but which at the same time is capable of limited rotation relative to the magnetic element, whereby the momentum of the damping device can opopse and cancel out the momentum of the magnetic element when the latter starts its reverse swing after initially overrunning the desired equilibrium point. As a result of this canceling or damping action, the magnetic element will come to rest almost instantaneously.

Other objects and many of the attendant advantages of the present invention will become readily apparent when reference is had to the following detailed specification which is to be considered together with the accompanying drawings wherein:

FIG. 1 is a side elevation of a plurality of indicator units of the type embodying the present invention, said indicator units being mounted on a common supoprting element with one of the indicator units being displayed in section;

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1; and

FIG. 3 is an exploded view showing the component parts of one of the indicator units of FIG. 1.

As illustrated in FIG. 1, a group of identical indicator units 2, each of which embodies the principle of the present invention, may be arranged in a single assembly or mechanical grouping. As indicated in FIG. 1, these individual units may be attached to supporting element 4 by means of a plurality of suitable standoff rods 6 which are threaded at both ends to receive nuts 8. The several units are uniformly spaced by means of spacer sleeves 1t) and spacer plates 12 which are mounted on rods 6. As will become more apparent from the description which follows, any selected indicia may be displayed by the respective units as a function of applied electrical excitation. The indicia chosen will be determined by the particular application. For example, each indicator unit 2 may be provided with all ten decimal digits, thereby allowing the apapratus of FIG. 1 to be used to furnish a visual digital output for an electronic counter. However, the display need not be digital in character, and any or all of the units 2 may be adapted to display alphatbetic symbols or any other special smbols that may be required by the apparatus into which the indicators are incorporated. Therefore, although in FIG. 1 digital presentation is illustrated, it will be understood that by relatively simple design changes, the principles of this invention may be extended to indicators capable of displaying grziater or fewer numbers or letters or other suitable symbo 5.

Each unit comprises a base plate 16 having holes 18 at its corners to accommodate the standoti rods 6. Attached to each base plate 16 is a toroidal coil unit generally identified at 29. Each toroidal coils unit 20 comprises a laminated toroid core which is formed of five separate segments 24, 26, 28, 30, and 32. The central element of the laminated toroid is a flat ring 24 having a circular configuration at its outer periphery. However, the inner periphery of ring 24 is formed into twelve adjacent teeth 26 which are symmetrically spaced. The function of the projecting teeth 26 is described below. This ring 24 may be economically stamped or otherwise fabricated from any material having good magnetic permeability, such as ordinary magnetic iron.

The toothed ring 24 is sandwiched between two identical rings 28 and 3t) which are made of soft iron and which have the same outer diameter as the ring 24. However, the inner diameter of the two iron rings 28 and 30 is somewhat greater than the imaginary circle which would be tangent to the points of all of the teeth 26. This leaves room for two identical aluminum rings 34 and 36 to be positioned on opposite sides of the teeth 26. The two rings 34 and 36 have an outside diameter equal to the inside diameter of the rings 28 and 30, and an inside diameter equal to the diameter of the aforementioned imaginary circles. Therefore, as viewed from one side or the other, the laminated structure appears to be a thick fiat ring which forms the core of the toroid coil structure.

Wound around each laminated core is an electric coil 40. Since the aluminum rings 34 and 36 are non-magnetic, the teeth 26 of ring 24 appear exposed, providing magnetizable, projecting prominences for coaction with the rotor magnet hereinaft r described. In the illustrated construction, each coil has twelve connecting leads 44 which are tapped off symmetrically around the coil and which are connected to external terminals by leads 46. By energizing different diametrically opposed leads 44, twelve :dilferent magnetic field orientations may be obtained. Each lead 4% is tapped at a point displaced a few degrees away from a radial line passing through each tooth point. In the illustrated device, the displacement of the leads is seen in FIG. 2 where two of the leads 44a and 44b are illustrated in phantom. With this construction, energization of any two diametrically opposed leads id will produce an electromagnetic field whose vector, indicated, for example, by the line X-X in FIG. 2, will correspond in general to a line between two diametrically opposed teeth 26 but which will be displaced from these two teeth by a few degrees. in this illustrated device, the displacement of the electromagnetic vector should be assumed to be approximately 9 degrees from the point of each of the teeth 26. This displacement is indicated by the aforementioned line X-X and line Y-Y, the latter being a line which passes between two diametrically opposed teeth.

The toroid unit is encased in plastic material t? as illustrated in FIGS. 13. Preferably, plastic material St) is of the same type of material as the base plate 16. For this reason, the coating 5% in FIG. 1 is shown as formed integral with the base plate 16. The use of plastic to attach the toroid unit to the base member 16 is convenient and advantageous for various reasons, such as providing a good hermetic seal from the atmosphere. Using the same type of plastic for both the base plate and the covering material for the toroid is advantageous in that it assures the formation or" a good bond between the two plastic sections.

in the illustrated embodiment, the supporting structures 4 also carry a mounting shaft 52. The length of the shaft 52 can be varied, depending upon how many of the units are to be assembled together. Although not shown, it is to be understood that each of the units may have individual shafts which may be coupled together by suitable coupling members. The manner in which the units are coupled together is immaterial insofar as the present invention is concerned.

Each operating shaft 52 supports a rotor assembly which comprises a central hub 54 which is rotatably mounted on the operating shaft by means of an intermediate bearing sleeve 56. One end of hub 54 is enlarged as shown at 58. Adjacent to this end the hub 54 has a peripheral fiange 60 and attached to this flange is an indicator element generally identified by the numeral 62 which is a disc 64 having a cylindrical flange 66 on which a series of numbers are secured. The numbers are arranged in successive fashion from zero to nine and are spaced apart by thirty-degree increments, thereby accounting for ten of twelve discrete positions on the flange corresponding to the twelve magnetic field orientations of the toroidal core unit 2%. The two vacant positions on the indicator 69 may be left blank or they may be used for other symbols. If they are left blank, then two pairs of leads 46 of the toroid coil unit will not be used, whereby the indicator element 62 will be positionable to display only the numbers from zero to nine.

It is to be observed that the indicator element disc 64 has a central aperture 68 which is sized to snugly receive the enlarged end 53 of the hub. The indicator element is brazed to the hub so as to rotate therewith. Rotatably mounted on the hub 54 is a cylindrical disk '70 having a center hole 72 Hub 54 extends through this center hole. This disk is separated from the enlarged flange 6% of the hub by means of a suitable spacer element '74. Also mounted on hub 54 is a second spacer '76 and a bar magnet '78. The adjacent end of hub 54 is swaged tight against the magnet so as to lock the latter tight against a shoulder formed on the hub. The magnet lightly engages spacer '76 and causes the latter to keep disk 70 in light sliding contact with spacer 7 With the foregoing arrangement, hub 54, indicator 2, and magnet 78 will rotate as a unit on shaft 52 and disk 70 is capable of rotation on hub 54.

As illustrated in FIG. 3, the disk '70 is provided with two holes 3-6 and 88 which are both mounted to one side of its center hole '72. Securely fastened in each of holes 86 and 88 is a pin 90. Mounted on each pin 96 is a coating or sleeve 92 made of a suitable resilient material such as rubber. The purpose of making the sleeve resilient is so that it will function as a cushion or shock absorbing element.

As indicated previously, disk 7% is rotatable on the hub, and, therefore, it is capable of rotation relative to the indicating element 62 and also the bar magnet 78. However, due to the fact that the disk '76 is provided with the two pins lid, the disk can rotate relative to the hub only within certain predetermined limits which are established by the bar magnet 78 and the pins 90. It is to be observed that in FIGS. 1 and 2. the bar magnet '78 is captured between the two pins 90. The spacing between the magnet and pins determines how much the disk 70 may rotate relative to the bar magnet and the hub. Preferably, this amount is approximately 5-15 degrees. However, the amount by which the disk may rotate relative to the magnet can be varied in accordance with the size of the unit and the torque applied to the bar magnet '78 by the applied electromagnetic field.

When the indicator element 62 is mounted as illustrated in FIG. 1, there will exist an annular spacing between its cylindrical flange 6d and the plastic coated toroid. This spacing is essential in order to permit ready rotation of the indicator element. In the same manner, the radial distance between the ends of the bar magnet and the axis of rotation is substantially less than the corresponding inner dimension of the toroid coil unit, thereby allowing the magnet to rotate freely within the toroid.

Referring now to FIG. 2, the operation of the improved indicator unit will now be discussed in connectlon with a viewing window 100 of a partition plate 1il2 which is located alongside the unit. Let it be assumed that the ends of the bar magnet are radially aligned with the numeral zero. With the device assembled and in operating condition, let it be assumed that a pair of diametrically opposed leads 44 are energized so as to cause an electromagnetic field which may be represented by the vector line X-X. The salient pole magnet 78 will rotate rapidly to align itself according to the selected magnetic field orientation; the sharply defined north and south poles of the magnet falling along the line XX. The toothed center element 24 of the core is sulficiently permeable that the energization of the electromagnetic structure causes magnetic saturization of the element 24. As the bar magnet swings by the points of the various teeth 26, the interaction between the magnet and the teeth is marginal and insignificant compared with the influence of the generated electromagnetic fields.

When the magnet is aligned with the line X--X, the selected character 3 will appear in the viewing window as slightly off center by approximately 9 degrees. The indir cator element 62 will remain in this position so long as 5 the current is on. However, if the energizing current is cut oil, the magnetic field designated by the vector XX will disappear. Then, since the salient poles of the magnet are displaced only a few degrees from the projecting teeth through which passes the line Y-Y, the attraction between these closely located teeth and the salient poles of the magnet will cause the magnet to rotate nine degrees to an equilibrium position represented by the vector Y-Y. This displacement will center the digit 3 within the viewing window 100.

The function of the disk 7t) is to bring the magnet 73 and the indicator element 62 to an immediate halt at the selected X-X position. In the absence of disk 70, there is a tendency for the magnet and the indicator element to overswing and to oscillate about the X-X position before stopping. With the disk added to the unit, the oscillating or hunting period of the magnet is reduced by a magnitude of four. When an input to the indicator causes the magnet to switch to a new position, the magnet will hit unstanding one of the pins 90, causing the disk to rotate with it to the new position. As indicated previously, when the magnet approaches and reaches its desired new equilibrium position, its momentum will cause it to continue past this new equilibrium position instead of stopping fast. However, due to the force exerted by the magnetic field, the magnet will then tend to reverse its direction so as to come back to the equilibrium position. Previously, when the magnet reversed its direction of travel, it would not only go back to the desired equilibrium position but would proceed beyond it. As a consequence, the magnet would thereafter have to reverse its direction again to come back to the equilibrium position. In practice, the magnet would overswing several times, thereby resulting in substantial elapsed time before it came to equilibrium. With the present invention, when the magnet reverses course or its initial overswing, it will strike the second or trailing pin on the disk '70 since the disk will still be moving in the original direction. The collision between this second pin and the magnet will cause the momentum of the disk acting in opposition to the magnet to rapidly reduce the overall momentum of the magnet bar system, thereby allowing it to be halted almost instantaneously by the stator attraction for the magnet.

First and foremost, it substantially eliminates hunting by the magnet and indicator element. Secondly, it does not significantly increase the size of the indicator unit. Another specific advantage is that it does not materially increase the cost. Fourthly, it entails no changes in the toroidal coil unit 20. Fifthly, it is useful not only when the power is turned oil after the indicator has been positioned at the desired point, but also when the power is maintained on throughout the display period of the selected digit or character. However, it is to be noted that for the latter type of operation, adjustments must be made so that the symbols or characters are symmetrically disposed in the viewing window 100 during periods of energization. The advantage of operating the device with the power on through the entire display period is that the residual or restraining torque is higher than that achieved under the conditions previously described. On the other hand, the disadvantage is large power consumption and a dependence upon power if a particular reading is to be retained for a considerable period of time.

Although the present invention has been shown with a toroid structure of the type illustrated in my foregoing copending application Serial No. 1,320, it is to be understood that the invention is not limited to any particular kind of toroidal stator structure. Thus, the damping means of the present invention may, for example, be utilized with the toroidal stator structure illustrated in the aforementioned Patent No. 2,943,313.

Obviously, many modifications and variations of the present invention are possible in the light of the foregoing teachings. It is to be understood, therefore, that the invention is not limited in its application to the details of construction and arrangement of parts specifically described or illustrated and that within the scope of the appended claims it may be practiced otherwise than as specifically described or illustrated.

I claim:

v1. A character indicating device comprising, a shaft, electrically energizable means for selectively establishing any one of a plurality of discrete non-coincident magnetic fields about said shaft, a magnet rotatably mounted on said shaft in position to be responsive to each of said noncoincident fields whereby said magnet will assume a different angular position for each of said fields, a character-bearing member connected to and rotatable with said magnet so as to assume a different display position for each different angular position of said magnet, and damping means rotatably mounted on said shaft for damping oscillatory motion of said magnet after it has shifted to any one of said difierent angular positions, said damping means comprising a disc rotatably mounted on said shaft, and two projecting pins on said disc coacting with said magnet to limit rotation of said disc relative to said magnet to a few degrees.

2. A character indicating device comprising, a shaft, electrically energizable means for selectively establishing any one of a plurality of discrete non-coincident magnetic fields about said shaft, a magnetrotatably mounted on said shaft in position to be responsive to each of said noncoincident fields whereby said magnet assumes a different angular position upon the establishment of each of said fields, a character-bearing member connected to and rotatable with said magnet so as to assume a different display position for each different angular position of said magnet, and damping means rotatably mounted on said shaft for damping oscillatory movement of said magnet after it has shifted to any one of said diiferent angular positions, said damping means comprising a disc rotatably mounted on said shaft and two projecting pins on said disc coacting with said magnet for limiting rotation of said disc relative to said magnet to a few degrees, said pins being oriented parallel to said shaft and spaced apart a distance greater than the distance between opposite side surfaces of said magnet.

References Cited by the Examiner UNITED STATES PATENTS 1,420,030 6/22 Ford 340319 1,922,759 8/33 Davis 3l0--49 2,435,709 2/48 Childs 340-498 2,665,343 1/54 Benson 340324 2,726,075 12/55 Hosford 340-498 X 2,943,313 6/60 Gordon et a1. 340-325 X FOREIGN PATENTS 214,031 10/09 Germany.

NEIL C. READ, Primary Examiner.

E. JAMES SAX, Examiner. 

2. A CHARACTER INDICATING DEVICE COMPRISING, A SHAFT, ELECTRICALLY ENERGIZABLE MEANS FOR SELECTIVELY ESTABLISHING ANY ONE OF A PLURALITY OF DISCRETE NON-COINCIDENT MAGNETIC FIELDS ABOUT SAID SHAFT, A MAGNET ROTATABLY MOUNTED ON SAID SHAFT IN POSITION TO BE RESPONSIVE TO EACH OF SAID NONCOINCIDENT FIELDS WHEREBY SAID MAGNET ASSUMES A DIFFERENT ANGULAR POSITION UPON THE ESTABLISHMENT OF EACH OF SAID FIELDS, A CHARACTER-BEARING MEMBER CONNECTED TO AND ROTATABLE WITH SAID MAGNET SO AS TO ASSUME A DIFFERENT DISPLAY POSITION FOR EACH DIFFERENT ANGULAR POSITION OF SAID MAGNET, AND DAMPING MEANS ROTATABLY MOUNTED ON SAID SHAFT FOR DAMPING OSCILLATORY MOVEMENT OF SAID MAGNET AFTER IT HAS SHIFTED TO ANY ONE OF SAID DIFFERENT ANGULAR POSITIONS, SAID DAMPING MEANS COMPRISING A DISC ROTTABLY MOUNTED ON SAID SHAFT AND TWO PROJECTING PINS ON SAID DISC COACTING WITH SAID MAGNET FOR LIMITING ROTATION OF SAID DISC RELATIVE TO SAID MAGNET TO A FEW DEGREES, SAID PINS BEING ORIENTED PARALLEL TO SAID SHAFT AND SPACED APART A DISTANCE GREATER THAN THE DISTANCE BETWEEN OPPOSITE SIDE SURFACES OF SAID MAGNET. 